Chiff and tone generator



Feb. 10, 1970 1'. w. CUNNINGHAM 3,495,021

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ATTORNEYj United States Patent Oihce 3,495,021 Patented Feb. 10, 1970 Int. 01. G101] 1/02, 3/00 US. or. s4-1.19 8 Claims This application is a continuation of my application Ser. No. 302,968, filed Aug. 19, 1963, now abandoned.

The present invention relates generally to electronic organs and more particularly to electronic organs having provisions for generating tonal characteristics which include chiff and other transient sound effects.

Perfection in electronic organs subsists, in the minds of some musicians, in the du lication of the tonal characteristics of pipe organs. Pipe organs inherently generate certain transient sound effects. These effects involve 1) a transient build up and decay of a spectrum of harmonics constituting a tone, with frequency shift in the course of the build up and decay, and (2) an audible tonal content occurring only at initiation of a note, and which may be harmonically or inharmonically related to the steady state spectral components, but which does not derive from the tonal build-up. The latter effect is called chiff.

It is, accordingly, a primary object of the present invention to provide a novel circuit for introducing chilf into the tonal output of an electronic organ.

It is another object of the invention to provide chiff circuitry for electronic organs in which chiff is generated by oscillators which are tonally independent of the ton generators of the organs.

A further object of the invention resides in the provision of a tone generating system for electronic organs, having provision for introducing a slow tone build up and decay with a concurrent frequency shift during the build up and decay.

Still another object of the invention resides in the provision of an electric organ in which tones are generated by connecting, in response to key switch closure, a constantly running tone generator to a high Q resonant circuit which is slightly detuned from the tone generator, and introducing desired harmonics into the response of the resonant circuit by means of distorting circuitry.

Still another object of the invention resides in the provision of an electronic organ in which is included means among the various harmonics, using the same high Q circuit for all the harmonics.

The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of one specific embodiment thereof, especially when taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 is a schematic circuit diagram of a basic circuit configuration according to the invention;

FIGURE 2 is a schematic circuit diagram of a modification of the system of FIGURE 1;

FIGURE 3 is a modification of the system of FIG- URES 1 and 2, in schematic form, including provision for chiff- FIGURE 4 is a wave form showing amplitude of chiif envelope as a function of time;

FIGURE 5 is a wave form of a tone and of chiff, showing relatively frequencies, amplitudes and timings;

FIGURE 6 is a schematic circuit diagram of a modification of the system of FIGURE 3 employing DC excitation of a chiff circuit;

FIGURE 7 is a block diagram of an organ system according to the invention;

FIGURE 8 is a block diagram of a modication of the system of FIGURE 3 employing a keyed on oscillator;

FIGURE 9 is a block diagram of a modification of the system of FIGURE 8, employing amplitude gated tones and chiff;

FIGURE 10 is a block diagram of a modification of the system of FIGURE 9, employing gated on tones deriving from a continuously running oscillator and chiif deriving from application of voltage to a chiif oscillator.

Referring now to the accompanying drawings, in FIG- URE l the reference numeral 10 denotes a continuously operative generator, of frequency 1 corresponding with the fundamental frequency of an organ tone. A key switch 11 in series with a relatively high resistance 12 connects the generator 10 to a tank circuit 13, comprised of inductance in parallel with a capacitance. One side of the tank circuit 13 is grounded. To the ungrounded side is connected an isolating amplifier 15. The latter in turn supplies output via a potentiometer 16 across a diode 17 and the latter drives parallel filters, 18, 19, 20, tuned respectively to pass the fundamental and various harmonies of the fundamental frequency 1, Certain of the higher order harmonics are programmed through broad band pass filter 22, rather than through narrow band-pass filters, and the filter 18 may be low pass if desired, cutting off just above the fundamental.

The tank circuit 13 is detuned, either above or below the frequency f by a increment A In operation, on closure of key switch 11, the tank circuit 13 is driven at frequency f and is also shock excited at frequency f-j-Af, where A represents detuning. The tank circuit 13 is a high Q circuit, and accordingly starts its current oscillation at the tank circuit resonant frequency f+Af. After a period of the transient, the frequency f-l-Af decays to zero and the tank circuit 13 then contains only current at the driving frequency When switch 11 is opened the tank circuit reverts to its natural frequency and signal at that frequency decays slowly to zero.

The AC voltage across the tank circuit is rectified by the diode 17. The harmonic structure of a diode-distorted sine wave can be very like that of a principal pipe of an organ. The filters 18, 19, 20, 22 are therefore not required to greatly modify the generated harmonic structure, and therefore simple filters may be employed, and in the limit filtering may be dispensed with.

The system of FIGURE 1, accordingly, produces a principal pipe tone, with relatively slow build up and decay, build-up and decay taking place slightly off true tone frequency f, and all harmonics generated by diode 17 participate in the off-true build up and decay transients.

Referring now to FIGURE 2 of the accompanying drawings, the reference numeral 20a denotes a generator of frequency 1, corresponding with the fundamental frequency of an organ tone. A key switch 21, when closed, transfers the signal across a resistance 22a (1K). The voltage developed across resistance 22 is transferred through a large resistance 23 (1M) to one end of a tank circuit 24, the coil 25 of which is center-tapped at 26, and the centertap grounded. There thus appears at the end terminals 27, 28 of tank circuit 24 AC voltages which are of opposite polarities. The tank circuit 24 is detuned from frequency f by Af, an amount (or percentage) appropriate to the desired tonal effect. The voltages at terminals 27, 28 are amplified in separate isolating amplifiers 30, 31 and the outputs of the latter ultimately combined at a common terminal 32.

In cascade with amplifier 30 is a capacitor 33 (.01) and a diode 34 and a resistance 35 (about 10K). A resistance 36 (K) is connected from the anode of diode 34 to ground and another resistance 37 (10K) from the cathode to ground.

The amplifier 31 is connected in cascade with isolating capacitor 39 (.01), a diode 40 in series with a variable 3 resistance 41 to the terminal 32. A resistance 43 (K) is connected between the cathode of diode 40 and ground. A bleeder resistor 42 (1-10 megohms) is provided for the capacitor 39.

The diode 34 introduces half-wave rectification, since its anode is relatively conductive to ground. The diode 40 introduces a transient half wave rectification, since its anode is relatively non-conductive to ground. By variation of resistance 41, the relative amplitudes of the two waves can be adjusted, so that the net voltage at terminal 32 represents adjustable peaks of half wave currents. If the two circuits were identical, the net voltage at terminal 32 would approach a full-wave rectified sine-wave, which has no odd order harmonics, and a complete set of even order harmonics. The effect, with a transient half wave signal, is a variable amount of even order harmonics and fundamental content versus time during the onset, i.e. as the potential of tank circuit 24 builds up.

The circuit of FIGURE 2 accordingly provides a simple device for varying the spectral constitution of a musical tone, in steady state, and particularly of generating a con tinuous variation during onset of the tone.

In FIGURE 3 of the drawings, a tone oscillator 50 drives a tank circuit 51, when key switch 52 is closed, resistances 53, 5'4 constituting respectively a load for oscillator 50 and a resistance for developing voltage representative to current into tank circuit 51. The voltage at tank terminal '56 drives an amplifier 57, which supplies isolation and gain. The tank circuit 51 is detuned with respect to the frequency of oscillator 50 by a few percent, as in FIGURES 1 and 2.

Amplifier 57 is coupled via DC isolating capacitor 58 and shunt resistance 59, and vice adjustable series resistance 60 to a pair of oppositely poled connected diodes 61, 62, each in series with a time constant circuit 63, 64. From diodes 61, 62, signal proceeds to output terminal 65. The diodes 61, 62 act as full wave clippers, the time constant circuits 63, 64 causing clipping, so that only peaks of half sine waves pass the diodes to ground.

Capacitors 66, 67 of time constant circuits 63, 64 charge as a function of time, with a speed determined by the value of variable resistance 60, until, when fully charged, the by-pass eflect is small and substantially full sine-wave currents How to terminal 65. Accordingly, two transient build-up or onset effects occur, one due to the high Q of tank circuit 51, and another due to the diodes 6'1, 62 and their associated timing circuits 63, 64. Moreover, during onset a transient frequency shift occurs at tank circuit 51, because it is detuned with respect to its driving frequency and a transient spectrum distortion occurs as the wave shape gated through by diodes 61, 62, varies. The steady state make-up of the spectrum arriving at terminal '65 can be varied, by varying the time constants of circuits 63, 64, between substantially pure sine waves and a square wave.

The AC signal deriving from resistance 53 is also applied over a channel A to a detector circuit 70 comprised of a diode 71-in series with a time constant circuit 72. The latter time is selected to provide fast but not in stantaneous build-up at point B, providing a positive voltage at that point. Voltage across resistance 59 is led to a further detector circuit 75, including a diode 76 and a time constant circuit 77, having a relatively slow build-up. Diodes 71 and 76 are poled to provide respectively positive and negative potential at point B, which is isolated from the diodes by large resistances 78, '79 (1M).

In operation, a positive voltage rapidly appears at point B, with a following negative voltage build up, which balances the positive voltage. The build up of negative voltage is slaved to the build up of current in tank circuit 51, so that when the latter attains steady state the net voltage at point B attains zero value. Discharge time constants for circuits 72, 77 are about equal, giving balance on decay after the key switch 52 is opened, i.e. both decay transients balance so that the net voltage at B remains zero.

The short positive pulse generated at point 'B on closure of key switch 52 is impressed at the grid 80 of a triode 81, connected in an RC oscillator circuit 82, conventional per se, and tuned to five and one half times the frequency (or any other frequency desired) of oscillator 50. The triode 81 is self-biased to non-oscillatory condition. When a positive pulse arrives at grid 80, the triode 81 and its associated oscillatory circuit 82 goes into oscillations until the positive pulse at B decays. These oscillations are applied to terminal 65.

The discharge time for circuits 72, 77 is such that rapidly repeated notes will not give a chiff except for the first attack. Complete recovery is long enough to allow a complete decay of the steady state tone, acting just as an organ pipe does.

The wave shape of the positive pulse at grid 80 of triode 81 is illustrated in FIGURE 4. Typical Wave shapes for the chili output of oscillator 82 is illustrated at 90, FIGURE 5, where 91 represents the wave form of the output of oscillator 50 as seen at terminal 65.

While the chiffcircuit of FIGURE 3 involves generation of keying pulse voltage for triode 81 in response to AC signal deriving from generator 50, it is preferable in some respects to derive the required pulse from a source of DC voltage in response to closure of a key switch, the latter switch being closed concurrently with closure of key switch 52 (FIGURE 3), on depression of a key of an organ keyboard.

Referring now to FIGURE 6, represents a source of DC voltage, the negative terminal of which is grounded and the positive terminal connected to a key switch 101, and a group of resistances in series 102 (270K), 103 (5.6 M), 104 (10K) back to ground. On closure of switch 101 substantially the entire voltage of source 100 appears across resistance 102. Connected across resistance 103 is a capacitor 105, and across resistance 104, a diode 106, having its cathode grounded. The anode of diode 106 is coupled via capacitor 107 to the cathode 108 'of a triode 109, having an unbypassed resistance connection 110 to ground. Triode 109 is connected in an RC oscillator configuration O, which is conventional per se, and hence is not further described, and which has an output resistance 111 coupled to the anode of triode 109. A variable tap 112 taken on resistance 111 applies a desired magnitude of oscillator output to a load 113. Arrows 114 indicate that further signal may be applied to load 113, for example the output of one or more of the main tone generators illustrated in FIGURE 7, 8 or 9, and which are capable of generating flute, principal or diapason reed tones. In general, oscillator O has a frequency of oscillation equal to about 5% times that of the main tone generator fundamental associated with it for stopped flute tone.

In operation, capacitor .1) charges through diode 106, charge current being limited initially by resistance 102, Most of the current supplied source 100 initially flows through diode 106, which then has a very low impedance, about 2000. The resistance 103 bleeds capacitor 105 after key 101 is released; a small resistance 104 10K) prevents leakage current during key-down state from holding the diode in a partially on state. While transient current is flowing through the diode 106, decreasing its resistance, the capacitor 107 'bypasses the cathode resistance 110. When capacitor 105 is fully charged, current flow through diode 106 terminates and diode 106 becomes high resistance, and therefore the lay-pass of resistance is removed. When the resistance 110 is lay-passed, the negative feed back of the oscillator 0 decreases and it oscillates. Normally, the negative feedback of resistance 110 prevents oscillation.

Discharge of capacitor 105 by resistor 103 is made slow enough that when key switch 101 is rapidly opened and closed, there is not suflicient current flow in diode 106 to trigger oscillator 0 into oscillation, giving the effect of a slow recovery time, as found in some organ pipes in respect to their chiff effects.

Describing now the general organization of an organ arranged according to the present invention, a gamut 200, of continuously running oscillators 201, 202, 203

is provided, one for each note of the musical scale. Separate gamuts 'may be provided for the different organ divisions, the illustration of FIGURE 7 pertaining to a portion of one such gamut only, the extension to a complete organ being deemed obvious.

The output of any oscillator, as 201, is applied to a key switch 205, which applies that output to a resonant tank circuit 206 having a high Q, and which is detuned by an amount Af, from the frequency f of oscillator 201. The extent of detuning, and whether the detuning shall be positive or negative, depends on the tone quality desired, or the instrument or stop to be simulated, For example, the resonant circuit is desired flat for principal and fiuate tones, and sharp for reed tones. Build up rates of the resonant circuits will also vary, according to the character of the tone involved, as 5 cycles for reed, cycles for principal and cycles for flute, at 131 c.p.s. steady state frequency.

It follows that closure of a key switch initiates build up of a transient in the resonant circuit, initially offset from the frequency of the driving oscillator, but after a few driving cycles, at that frequency only. The resonant circuit drives a harmonic generator 207, various forms of which may be employed depending on the character of the tone to be generated, as flute, reed, diapason, etc., and the output of the harmonic generator is then filtered in a tone color filter 208. The influence of the resonant circuit in generating detuned transients is thus felt at the harmonic generator, which also provides transient harmonics, i.e. a build-up of amplitude, during which change of tone frequency occurs, simultaneously but not identically for all the harmonics.

Simultaneously with, or at least substantially at the same time as, key switch 205 is closed, an associated ganged key switch 209 is closed, which applies DC voltage to a pulse generator 210 on closure. The pulse sets a chiif oscillator 211 into oscillation, for the duration of the pulse, at 5 /2 times the frequency of the associated tone oscillator. The output of chiff oscillator 211 and of tone color filter 208 are combined and acoustically radiated in a speaker 212, after suitable amplification in an amplifier 213.

Similar circuits for generating transient build up of tone, for generating harmonics, and for generating chiff, are employed for all tones, i.e. in conjunction with each of tone oscillators 201, 202, 203.

The tone generators systems themselves are individually designed to generate the required transient build up characteristics in both amplitude, frequency and harmonic content, and to generate the required steady state harmonic structure for the tone color desired, especially when employed in conjunction with suitable tone color filters.

A great many variations are possible without changing the basic principles of this invention, such as using keyed on generators along with the chiif circuits rather than continuously running generators, and the use of other resonant circuit configurations which give similar results. Using a keyed on generator or a continuously running generator that has been amplitude gated and switched into the high Q build-up circuit can give even more desirable transient amplitude envelopes, as well as different pitch transients.

For example, in the system of FIGURE 8, the tone oscillator 250 is keyed into operation on closure of key switch 251, by application thereto of operating voltage from a source 252. The system may in other respects duplicate FIGURE 6, so that the distinction between FIGURES 8 and 6 may be essentially that in FIGURE 6 a continuously running tone oscillator is employed, whereas in FIGURE 8 a keyed on tone oscillator is employed.

In the system of FIGURE 9, on the other hand, a continuously operating chitf oscillator 260 and a keyed on tone oscillator 261 are gated into the organ system by means of amplitude gates 262, 263, which shape the envelopes of the tone and chiff, respectively, when key 264 isclosed, according to wave shapes provided by gate wave generators 265, 266. In particular as concerns the tone, the wave shape applied to the high Q resonant circuit 267 is pre-shaped in respect to rise and decay. In consequence, greater control over tone envelope is achieved than is easily feasible when shape is achieved solely by Q control of circuit 267.

In the system of FIGURE 10, the chifl circuit of FIG- URE 3 is referred to, a continuously operating tone oscillator 270 is employed, and gating circuit 271, 272 rather than a keyed on oscillator, as 261 of FIGURE 9.

While I have described and illustrated one specific embodiment of my invention, it will be clear that variations of the details of construction which are specifically illustrated and described may be resorted to without departing from the true spirit and scope of the invention as defined in the appended claims.

I claim:

1. A transient and tone generating system for an electronic organ, comprising (a) a source of a tone signal having a fundamental frequency,

(b) a normally inoperative oscillator tuned to a frequency different from the said fundamental frequency,

(c) a resonant circuit detuned with respect to said fundamental frequency,

(d) key switch means for connecting said source to said resonant circuit and for transiently rendering said oscillator operative only during onset of said tone,

(e) an output system,

(f) a wave modifying circuit connected intermediate said resonant circuit and said output system for generating harmonics in response to said tone signal, and

(g) means connecting said oscillator to said output system.

2. In an organ system,

a tone oscillator,

a high Q resonant electrical system,

a key operated switching device intermediate said tone oscillator and said high Q resonant electrical system, said high Q resonant electrical system being audibly detuned with respect to said tone oscillator and having a time constant of audible duration, whereby on operation of said switching device said tone oscillator is connected to said high Q resonant electrical system and transient response at one frequency and steady state response at another frequency build up audibly in said high Q resonant system, and

electro acustic radiating means responsive to the total transient response of said system, wherein a harmonic generating circuit is interposed between said high Q resonant electrical system and said radiating means.

3. The combination according to claim 2 wherein is provided a chiif generator operator operatively associated with said switching device and operative in response thereto, said chiff generator including a resonant device, means for on-gating said chiff generator transiently in response to operation of said switching device in accordance with a gating law including relatively audibly slow build up and decay.

4. In an electrical musical instrument: a set of substantially sine wave generators for producing electrical signals corresponding to notes in a musical range; a frequency shift channel having means shifting the nominal frequency of signals applied thereto; means for deriving electrical signals from said generators and applying them 7 to said shift channel; and means operatively associated with said shift channel for adding harmonics to the signals shifted in frequency.

5. In an electrical musical instrument: a set of substantially sine wave generators for producing electrical signals corresponding to notes in a musical range; circuit means for adding harmonics to signals; and means for connecting the generators to the circuit means, including means for altering the nominal frequency of the signals.

6. In an electrical instrument: a set of substantially sine wave generators for producing electrical signals corresponding to notes in a musical range; an output channel; and a circuit between each of the generators and the output channel including means for shifting the nominal frequency of the generated signal, and means for imparting harmonics to the frequency shifted signal.

7. In an electrical musical instrument,

a tone generator having a frequency f, in the musical range,

a key switch connected in cascade with said tone generator,

a resonant circuit having a resonant frequency f-i-Af connected in cascade with said key switch, where A is a small increment in f,

a harmonic generator connected in series with said resonant circuit, and

output means connected in cascade with said harmonic generator.

8. In an electrical musical instrument,

a tone generator having a frequency f in the musical range,

a key switch,

a resonant circuit having a resonant frequency f-l-Af,

where A is a small increment in 1,

means responsive to closure of said key switch for connecting said tone generator in cascade with said resonant circuit,

a harmonic generator connected in cascade with said resonant circuit, and

output means connected in cascade with said harmonic generator.

References Cited UNITED STATES PATENTS 6/1922 Markovitz 84-124 6/ 1961 Markovitz 841.26 X

US. Cl. X.R. 

1. A TRANSIENT AND TONE GENERATING SYSTEM FOR AN ELECTRONIC ORGAN, COMPRISING (A) A SOURCE OF A TONE SIGNAL HAVING A FUNDAMENTAL FREQUENCY, (B) A NORMALLY INOPERATIVE OSCILLATOR TUNED TO A FREQUENCY DIFFERENT FROM THE SAID FUNDAMENTAL FREQUENCY, (C) A RESONANT CIRCUIT DETUNED WITH RESPECT TO SAID FUNDAMENTAL FREQUENCY, (D) KEY SWITCHMENS FOR CONNECTING SAID SOURCE TO SAID RESONANT CIRCUIT AND FOR TRANSIENTLY RENDERING SAID OSCILLATOR OPERATIVE ONLY DURING ONSET OF SAID TONE, (E) AN OUTPUT SYSTEM, (F) A WAVE MODIFYING CIRCUIT CONNECTED INTERMEDIATE SAID RESONANT CIRCUIT AND SAID OUTPUT SYSTEM FOR GENERATING HARMONICS IN RESPONSE TO SAID TONE SIGNAL, AND (G) MEANS CONNECTING SAID OSCILLATOR TO SAID OUTPUT SYSTEM. 